Abstract:
BACKGROUND : Rotheca glabrum (formerly known as Clerodendrum glabrum [Verbenaceae]) is used by local communities
in the Limpopo Province of South Africa to control ticks on livestock and was selected from the database of the ARCOnderstepoort
Veterinary Institute. Its leaves were extracted using organic solvents ranging from polar to non-polar
solvents (methanol, acetone and dichloromethane (DCM)). In addition, the traditional soap-water (infusion) and waterbased
(decoction) methods were used. The tick repelling activity was determined against the adult stage of the
livestock tick Rhipicephalus appendiculatus.
RESULTS : In the tick-climbing repellency bioassay a 30% acetone extract had a significant (p ≤ 0.05) repellent effect
against adults of R. appendiculatus. The extract was still active at a lower concentration of 10%. The hexane fraction
from the R. glabrum acetone extract had a higher tick repellency activity than the positive controls Amitix and Bayticol
at the same concentrations. Unfortunately, the activity decreased after 2.5 h, probably due to volatility of the
biologically active compound(s) within the extract.
CONCLUSION : Attempts were made to isolate the repellent compound from the acetone extract of R. glabrum. The
process produced very good results up to a late stage in the bioassay-guided fractionation process. At that point,
the repellent activity was lost. When two fractions were combined, the repellent activity was regained. These results
provide strong evidence for the existence of a synergisticactivity of different compounds. It may be better to
concentrate on extracts that would kill ticks rather than on extracts that would repel ticks.
